#include <stdio.h>

//https://www.nowcoder.com/practice/ce0b2eacd3d04647831358c2876e44ff?tpId=290&tags=&title=&difficulty=0&judgeStatus=0&rp=0&sourceUrl=%2Fexam%2Foj%2Fta%3FtpId%3D290

int main() {
    long num = 0;
    long sum = 0;
    scanf("%ld", &num);
    do {
        sum += num;
    } while (num--);
    printf("%ld", sum);
    return 0;
}
